The invention relates to a printing-machine cylinder, especially an impression cylinder, for a sheet-fed rotary printing machine, and to a method for producing such a printing-machine cylinder.
When sheets are being transported through a sheet-fed rotary printing machine, they are printed in a conventional manner in a printing nip formed between an impression cylinder and an associated blanket cylinder, and are then fed, by one or more transfer cylinders, to a downstream printing unit or a reversing or turning device. In order to prevent smearing of the freshly printed side of the sheet on the transfer cylinders, it has become known heretofore to provide openings in the peripheral surface of the cylinders, through which blast air is blown for carrying the sheets on the peripheral surface of the transfer cylinders without smearing.
Both in the case of the sheet transfer cylinders described above and in the case of impression cylinders of sheet-fed rotary printing machines which are assigned to a reversing device, and in which, during first-form and perfecting operation, the sheets are carried on the upline impression cylinder and the trailing edge of the sheets is accepted by a gripper device of the downline transfer cylinder, it has become known heretofore to suck the sheet onto the peripheral surface of the cylinder in order to hold it on the peripheral surface.
The published non-prosecuted German Patent Application (DE-OS) 41 26 643 A1 discloses a transfer cylinder for a sheet-fed rotary printing machine having a basic cylinder body formed by four supporting disks whereon a total of three supporting elements are fastened. Each of the supporting elements has a sandwich-like construction, at the center of which, suction chambers are defined by a metal sheet folded in a serpentine manner and covered towards the outside of the cylinder by a sheet-metal covering having a thin wall and curved so as to correspond to the curvature of the cylinder. Each of the chambers has a flow connection to the environment via associated openings in the sheet-metal covering, and can have suction air applied thereto via a rotary valve, in order to suck a sheet onto the peripheral surface of the cylinder and smoothen it. Because of the thin-walled folded metal sheet used to form the chambers, and the associated sandwich-like construction of the cylinder, the latter is not suitable for use as an impression cylinder in a printing unit of a sheet-fed rotary printing machine.
The published European Patent Document EP 0 165 477 B1 has disclosed a sheet-fed rotary printing machine with a reversing or turning device having an impression cylinder arranged upline of the reversing device and onto which the sheets to be reversed or turned are sucked and held. The impression cylinder has a solid basic body, in which suction-air or blast-air feed channels, which extend axially over the entire width of the cylinder, are formed. From each of the feed channels, a multiplicity of radial holes or bores extend to the peripheral surface of the basic cylinder body. In addition, a textured film is drawn onto the peripheral surface of the basic cylinder body and, in the region of the radial bores, is porous or is formed with openings through which a sheet transported on the cylinder can be sucked against the peripheral surface and lifted off the latter, respectively. From this published. European patent document, it is also known to provide a transfer cylinder, that is constructed as a storage drum and is covered with a porous film, with a suction box that can be moved so as to adapt it to different sheet formats and that sucks the trailing edge of a sheet to be reversed or turned, against and onto the peripheral surface of the transfer cylinder. Because of the feed holes, which extend in the axial direction over the entire width of the impression cylinder, and the numerous fine radial holes or bores to be introduced into the peripheral surface of the basic body of the impression cylinder, the production of the described impression cylinder proves to be extremely complicated and costly.
Because of the comb-like or finger-like configuration of the peripheral surface of the transfer cylinder, that is associated with the ability of the suction box to be moved, the transfer cylinder is not suitable likewise for use as an impression cylinder in a sheet-fed rotary printing machine, because the comb-like structure of the peripheral surface is transferred to the printed image and has a lasting detrimental effect upon the latter.
It is accordingly an object of the invention to provide a printing-machine cylinder, especially an impression cylinder for a sheet-fed rotary printing machine, that is simple and inexpensive to produce and that permits sheets carried on the cylinder to be both sucked onto it and blown off it.
Furthermore, it is an object of the invention to provide a production method by which a printing-machine cylinder, especially an impression cylinder of a sheet-fed rotary printing machine that has a peripheral surface provided with blast or suction openings, can be produced in a simple and more cost-effective manner.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a printing-machine cylinder comprising a basic cylinder body and a covering element fitted to the basic cylinder body, one of the basic cylinder body and the covering element being formed with a multiplicity of recesses connectable to one of a suction-air source and a blast-air source and having, in the region of the recesses, through-channels extending from the recesses to the peripheral surface of the covering element and defining blasting/suction sections for acting upon the underside of a sheet conveyed on the peripheral surface of the cylinder.
In accordance with another aspect of the invention, there is provided a printing-machine cylinder comprising a basic cylinder body having a multiplicity of recesses formed therein and being connectable to one of a suction-air source and a blasting-air source, and having a covering element fitted to the basic cylinder body and, in the region of the recesses, being formed with through-channels extending from the recesses to the peripheral surface of the covering element and defining blasting/suction sections for acting upon the underside of a sheet being conveyed on the peripheral surface of the cylinder.
In accordance with a further aspect of the invention, there is provided a printing-machine cylinder comprising a basic cylinder body, and a covering element fitted to the basic cylinder body and formed on the inside thereof with a multiplicity of recesses connectable to one of a suction-air source and a blast-air source and, in the region of the recesses, being formed with through-channels extending from the recesses to the peripheral surface of the covering element, and defining blasting/suction sections for acting upon the underside of a sheet conveyed on the peripheral surface of the cylinder.
In accordance with another feature of the invention, the through-channels have a section of relatively larger diameter and a section of relatively smaller diameter.
In accordance with a further feature of the invention, the section of relatively larger diameter is formed as a bore in the covering element and extends in a direction from the center of the cylinder.
In accordance with an added feature of the invention, the blasting/suction sections are arranged substantially in rows on the peripheral surface of the cylinder.
In accordance with an additional feature of the invention, the rows extend substantially parallel to one another.
In accordance with yet another feature of the invention, the rows extend in the axial direction.
In accordance with yet a further feature of the invention, as viewed in the direction of rotation of the cylinder, the rows are of decreasing length.
In accordance with an added feature of the invention, the rows extend in the peripheral direction.
In accordance with yet an additional feature of the invention, the rows extend substantially in a V-shape or ray shape.
In accordance with still another feature of the invention, the printing-machine cylinder includes a connecting line for applying one of suction air and blasting air in common to the recesses assigned to a row.
In accordance with still a further feature of the invention, the printing-machine cylinder includes valves assigned to the recesses for connecting the recesses, individually or in groups, to the one of the suction-air source and the blasting-air source.
In accordance with still an added feature of the invention, the recesses are subjectible to the application of said one of suction air and blast air depending upon the sheet format to be processed, in a manner that only the blasting/suction sections underneath a sheet conveyed on the cylinder have the one of suction air and blast air applied thereto.
In accordance with still an additional feature of the invention, the printing-machine cylinder includes a control device for controlling a feeding of the one of suction air and blast air to the recesses.
In accordance with another feature of the invention, all of the recesses are connectable simultaneously to the one of the suction-air and blast-air sources via the control device.
In accordance worth a further feature of the invention, the through-channels in the covering element have a cross section widening in a direction towards the recesses.
In accordance with an added feature of the invention, the peripheral surface of the covering element has a porous film applied thereto, wherein those sections of the through-channels which have a relatively smaller diameter are formed.
In accordance with an additional aspect of the invention, there is provided a printing machine having the cylinder that is formed as an impression cylinder arranged upline of a reversing device, the control device, during first-form and perfecting operation, serving to connect the recesses, in a region between a printing nip and a transfer center line between the impression cylinder and a downline sheet-carrying cylinder, to the suction-air source, in order to hold the sheets on the peripheral surface of the cylinder.
In accordance with another feature of the invention, the control device, during first-form and perfecting operation, serves to connect the recesses, in a transfer region that as one of directly upstream and directly downstream of the transfer center line and wherein a trailing edge of the sheet is acceptable by a gripper device of a downline sheet-carrying cylinder, to the blast-air source.
In accordance with a further aspect of the invention, there is provided a printing-machine cylinder comprising a basic cylinder body and an air-permeable, porous covering element fitted to the basic cylinder body and having a multiplicity of interconnected channels formed therein, the channels being connectable to one of a suction-air source and a blast-air source via air feed lines for sucking a sheet carried on the cylinder onto the peripheral surface of the cylinder or for lifting the sheet off the peripheral surface of the cylinder.
In accordance with an added feature of the invention, the air feed lines are formed in the basic cylinder body.
In accordance with an additional feature of the invention, as viewed in the direction of rotation of the cylinder, during first-form and perfecting operation, the control device serves to connect the recesses, in the region between a transfer center line between the cylinder and a downline sheet-conveying cylinder and a printing nip, to the blast-air source, so as to detach the sheets from the peripheral surface of the cylinder.
In accordance with yet another aspect of the invention, there is provided a method for producing a printing-machine cylinder, which comprises the steps of making a basic cylinder body ready; forming recesses in a peripheral surface of the basic body; introducing at least one air-supply bore into the recesses; fitting a cylinder covering element to the basic cylinder body, the cylinder covering element having, in the region of the recesses, a multiplicity of through-channels extending from the recesses to the peripheral surface of the cylinder covering element.
In accordance with yet an added aspect of the invention, there is provided a method for producing a printing-machine cylinder, which comprises the steps of making a basic cylinder body ready; making a cylinder covering element ready; forming recesses in the inside of the cylinder covering element; introducing into the cylinder covering element a multiplicity of through-channels, extending from the recesses to the peripheral surface of the cylinder covering element; forming at least one air-supply bore in the basic cylinder body; and fitting the cylinder covering element to the basic cylinder body.
In accordance with another mode, the method of the invention includes the further step of applying a porous film or foil to the peripheral surface.
In accordance with an additional aspect of the invention, there is provided a method for producing a printing-machine cylinder, which comprises the steps of providing a basic cylinder body; introducing an air-feed line into the peripheral surface of the basic cylinder body; and fitting a porous, air-permeable cylinder covering element to the basic cylinder body.
In accordance with another feature and mode of the cylinder and the method of the invention, the cylinder is an impression cylinder for a sheet-fed rotary printing machine.
In accordance with a concomitant feature of the printing machine of the invention, the printing machine is a sheet-fed rotary printing machine, and the cylinder is an impression cylinder.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a printing-machine cylinder, especially an impression cylinder, for a sheet-fed rotary printing machine, and a method of production thereof, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.